The customer noticed the data rate is not fixed and the no. will range from 23MB/s to 27MB/s.
On the other system with Blackmagic, this does not happen.
I remembered on other systems with Kona cards, the data rate does not change too.

Both Kona and Blackmagic systems are working on PAL Uncompressed 10bit only.

Ben -
your dropped frames are due to a drive issue. Run AJA Kona System Test on the HUGE array, and report back your results, in read and write speeds in mb/sec. This will help determine what is going on. I am not there, and for all I know, you client is trying to record on the internal hard drive of the MAC.